carb cleaning ?

Category: 912 / 914 Technical Questions one month ago

intermittant power in flight advice is to clean carbs for debris clogging passage. (have replaced floats, replaced fuel filter, checked vent line position, checked P-leads for chafe/grounding, gravity fuel flow test) 

last flight - start up, taxi and run-up were great, then initial take-off good until a few hundred feet then severe cutting out, ran decent with lower power setting to get to downwind landing, then ran fine for short final and taxi to hanger. Also, checked front two spark plugs, they are white.

Does anybody know of a video or any instruction on checking carbs ?


dan dawson 563-349-4059

  • Re: carb cleaning ?

    by » one month ago

    What engine??

    If its the 914, then you are probably leaking boost pressure out of your carb float bowl gaskets!


  • Re: carb cleaning ?

    by » one month ago

    oops forgot to mention its a 912S.

    have a new theory that a manifold air leak could cause strange intermittant fluctuations ? unsure how to check. Surprised it doesnt run bad all the time. 

    have problem of nearest Rotax mech is 150 mi away, don't want to remove and dissassemble carbs if thats not the cause.

  • Re: carb cleaning ?

    by » one month ago

    It is unlikley that  BOTH carbs have EXACTLY the same problem.

    If one carb were to have a major problem the engine would be shaking like crazy because the other side would still be making full power.

    Your problem is much more likely to be a fuel supply problem (White Plugs) common to both carbs.

    Do you have a fuel pressure gauge?  AUX Fuel Pump?  Clean Tank Sumps (Water?)? 

    Check the fuel filters. (Limited/Restricted flow)

    You made full power for long enough to get it well into the air then ran out of full power but maintained lower power levels.

    I would move carb cleaning a few notches down the hit list until other theories are ruled out.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated.

  • Re: carb cleaning ?

    by » one month ago

    What Bill said. :)  Sounds like fuel supply issue.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

  • Re: carb cleaning ?

    by » one month ago

    Where does your mechanical fuel pump vent line terminate? It must not be exposed to the external slipstream. Where do your individual carburetor vent lines terminate? They must not be exposed to the external slipstream.

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